1. Field of the Invention
The present invention relates to a novel method allowing a more effective and cheap tight jointing between a sleeve and a submarine pipe laid at a great depth. More specifically, the invention relates to an improvement to the method already disclosed in our prior U.S. Pat. No. 4,388,752 granted on June 21, 1983.
2. Description of Background Art
It is known that, according to the method of said U.S. Pat. No. 4,388, 752 the tight fastening of a cylindrical sleeve of constant cross-section area to a steel pipe comprises the successive steps of inserting inside the overlapped pipe-sleeve assembly a particular plug expander of hard rubber, of axially compressing said plug in order to radially expand said pipe-sleeve assembly up to the limit of elastic strain of the material constituting the sleeve, which is higher than that of the pipe, and of decompressing and extracting said plug from said pipe.
It is clear now that if it were possible to adopt, instead of a cylindrical sleeve of constant cross-section area, a cylindrical sleeve having its inner surface shaped with a series of grooves and of toothings, the double result of a more effective and cheap tight joining between the sleeve and the pipe would be accomplished.
In fact, during the said radial expansion the pipe would penetrate into the grooves of the sleeve, and would hence remain fastened to this latter, thus considerably enhancing the resistance to the axial thrusts, which in the case of a cylindrical sleeve with constant section is entrusted to friction only.
On the other hand, whilst in the case of the cylindrical sleeve with constant cross section area the pipe must be submitted to mechanical machining before the jointing, in order to remove the outer longitudinal welding bead, whose presence would compromise the tightness. In the case of the sleeve provided with a toothing this would not occur, in that the outer welding bead would get squashed against the edge of the teeth: the mechanical turning of the submarine pipe would thus be avoided, which is very difficult to be done in the case of very great depths and would require a long time and high expenses.
Unfortunately, in the high depth submarine applications, the adoption is made impossible by the high pressure of the water present in the slots, which prevents the pipe from expanding into said slots.
A method which would allow a cylindrical sleeve of not constant cross section area to be adopted could consists in providing holes in correspondence of the slots of the sleeve, in order to allow the outflow of the water during the expansion of the pipe, but such a solution would weaken the sleeve and consequently would considerably decrease the tightness safety.